1. Field of the Invention
The present invention relates to a three-dimensional measurement method for measuring a shape of an object in a non-contact manner and a three-dimensional measurement system using the method.
2. Description of the Related Art
As non-contact three-dimensional measurement means, an optical three-dimensional digitizer is known that uses a triangulation method such as a stereo vision method or a light-section method. Such a three-dimensional digitizer can digitize a shape of an object placed within the field of view by one-time measurement. For example, Japanese unexamined patent publication No. 2002-31511 describes measuring an object using a three-dimensional digitizer. On this occasion, the position of the three-dimensional digitizer is changed such that the object is viewed from the front, back, left or right side. In this way, shape data of the entire periphery of the object is obtained. Further, Japanese examined patent publication No. 6-8730 describes a method for measuring a reference point of a work using an optical distance sensor attached to a tip of a robot arm to correct fixing error of the work.
In contrast, with respect to contact three-dimensional measurement, measurement is automated in which a numerical controller is used to move a probe (sensing pin) automatically along an object surface. Japanese patent No. 2741518 describes a related art concerning the automation. More specifically, before substantial measurement in which a probe is automatically moved, preliminary measurement is performed in which the probe is moved by a manual operation in order to detect positioning error of an object to be arranged at a predetermined position. Then, depending on the detection result of the positioning error, a moving start point of the probe in the substantial measurement is modified.
As for contact measurement devices, even if an arrangement position of an object is significantly deviated from a correct position, it is desirable that preliminary measurement should be performed manually to prevent a probe from failing to contact the object or from pressing against the object excessively.
As for non-contact three-dimensional measurement, it is likely that a movement mechanism capable of operating by numerical control is used to automatically change a position and a posture of a three-dimensional digitizer. The automation enables rapid and efficient measurement without omission.
In the case where an approximate shape of an object is known, for example, when the object is a product designed by CAD (Computer Aided Design), or, when the object is a replication of a sample or a primary standard, it is desirable that teaching should be conducted as is the case with industrial robots. A measurement path most suitable for a shape of an object is set by off-line teaching based on an imaginary object shown by CAD data or by direct teaching based on an actual object such as a sample or a primary standard. In this way, measurement accuracy is enhanced.
A problem arises, however, that an object needs arranging to take a posture determined to be a set position in the teaching in order to realize desired accuracy.